Optical systems having optical elements generally have an axis about which all of the optical elements of the optical system are constructed symmetrically. The aforementioned axis is designated as the optical axis of the optical system. The optical elements are constructed in rotationally symmetrical fashion.
An anamorphic objective, which likewise has optical elements, has no such axis as axis of symmetry. Rather, the anamorphic objective has at least one plane of symmetry about which at least some of the optical elements of the anamorphic objective are constructed in mirror-symmetrical fashion.
The system described herein relates to an anamorphic objective having two planes of symmetry, namely a first plane of symmetry and a second plane of symmetry. The first plane of symmetry is arranged perpendicular to the second plane of symmetry. The anamorphic objective has at least one lens element having a surface constructed in mirror-symmetrical fashion with respect to the first plane of symmetry and the second plane of symmetry. Such a lens element can be designated as an anamorphic lens element. The designation anamorphic optical element can be chosen as a different designation, for example, for said lens element.
The aforementioned surface of the anamorphic lens element can also be designated as an anamorphic surface. The latter is distinguished by the fact that it has a first curvature in the first plane of symmetry and a second curvature in the second plane of symmetry. The first curvature and the second curvature can be different. If the first curvature and/or the second curvature are/is zero (or infinite), then the anamorphic surface is cylindrical. If the first curvature and the second curvature are different, but have the same sign, then the anamorphic surface is embodied in toric fashion. If the signs are different from one another, then the anamorphic surface is a saddle surface.
The anamorphic optical element has a first refractive power with respect to the first plane of symmetry and a second refractive power with respect to the second plane of symmetry. The first refractive power can be different from the second refractive power.
The first plane of symmetry and the second plane of symmetry intersect and have a straight line of intersection (that is to say an intersection line). Said intersection line forms an optical axis of an optical element of the anamorphic objective. Since the anamorphic objective is generally composed of a plurality of optical elements, the plurality of optical elements in each case have an optical axis, which, however, generally overlap and form a common optical axis. This common optical axis is the optical axis of the anamorphic objective.
Anamorphic objectives which can be classified in three categories are known from the prior art.
A first category concerns objectives with an anamorphic supplementary system. Such objectives are known from DE 36 29 438 A1 and U.S. Pat. No. 4,362,366 for example, which are incorporated herein by reference. An anamorphic supplementary system generally has a plurality of lens groups separate from one another. One disadvantage of the objectives of this category is that the anamorphic supplementary system generally has a large diameter and also a large mass. The anamorphic supplementary system is therefore quite heavy. Furthermore, it has been found that focusing is difficult to carry out in the case of objectives of this category.
A second category of objectives concerns objectives comprising at least two subsystems. A first subsystem is embodied as a rotationally symmetrical objective comprising a plurality of lenses arranged successively in the direction of an image acquisition unit as seen from an object. A further subsystem comprising an anamorphic optical element is arranged between a last lens element of the rotationally symmetrical objective and an image acquisition unit. Such an objective is known from US 2006/0050403 A1 for example, which is incorporated herein by reference.
A third category of objectives concerns anamorphic objectives having at least one first lens element and at least one second lens element. At least one anamorphic optical element is arranged between the first lens element and the second lens element. Such an arrangement of an anamorphic objective is known, for example, from DE 10 2008 021 341 A1, which is incorporated herein by reference.
If the imaging of an axial object (that is to say of an object on the optical axis) by means of an anamorphic optical element is considered, then, it is established that this imaging is paraxially astigmatic. This means that image point positions of the imaging of the axial object in the first plane of symmetry and the second plane of symmetry are differently remote from the anamorphic optical element. The image point positions in the first plane of symmetry and second plane of symmetry are accordingly at a different distance from the anamorphic optical element.
By contrast, if the imaging of an axial object by means of a rotationally symmetrical optical element is considered, it is established that the imaging of the axial object is paraxially stigmatic. This means that a point embodied as an axial object is imaged onto an imaging point. However, the imaging of an abaxial object (that is to say an object which is not axial) by means of a rotationally symmetrical optical element can be astigmatic owing to aberrations present.
When taking a photograph, when recording an image for a film recording and/or when projecting an image or a photograph, an astigmatic imaging by means of an objective is not desirable. Rather, it is endeavored to achieve a stigmatic imaging by means of an objective for the aforementioned applications, since a stigmatic imaging leads to a better image quality.
Accordingly, it would be desirable to address the problem of specifying an anamorphic objective suitable for generating a stigmatic imaging of an object on an image acquisition unit.